Method of producing aldehydes

Details Method of producing aldehydes Method of producing aldehydes

1999-12-03

2003-08-26

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S454000, C502S158000

Reexamination Certificate

active

06610891

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a method of producing aldehydes. More particularly, the present invention relates to a method of producing aldehydes using a hydroformylation reaction wherein the formation of high boiling point components and decomposition of the catalysts, and in particular the ligand are minimized. The aldehydes produced may be an end product, or alternatively may be an intermediate product employed in further processing.
BACKGROUND OF THE INVENTION
The production of aldehydes is an important process in the chemical industry. Aldehydes are widely used for a variety of purposes, for example as a precursor for the formation of 2-ethyhexanol (2EH) which is an important raw material for plasticizer, or upon subsequent hydrogenation to form alcohols. Aldehydes may be produced by a variety of methods. One important production method is hydroformylation. The hydroformylation reaction basically combines an alkene with carbon monoxide and hydrogen, in the presence of a catalyst, to form an aldehyde of one carbon number higher than the feed alkene. For example, the hydroformylation of propylene forms butyraldehydes, also referred to as C4 aldehydes. Examples of some prior art hydroformylation processes are described in U.S. Pat. Nos. 4,599,206; 4,748,261; 4,885,401; 5,059,710; 5,288,918; 5,648,553; 5,663,403; and 5,672,766.
In general the prior art hydroformylation systems typically involved the production of aldehydes, and optionally alcohols by further hydrogenation of the aldehydes, by reacting an olefinic compound with hydrogen and carbon monoxide in the presence of a catalyst, most often a metal organophosphorus ligand compound catalyst. A solvent may be employed to dissolve and disperse the reactants in solution thereby providing a reaction solution. The prior art systems are typically a liquid recycle system, that is at least a portion of the reaction solution is withdrawn from the hydroformylation reactor containing aldehyde products along with remaining reactants and catalyst either continuously or periodically. The aldehyde products, and optionally one or more of the reactants and catalyst, are separated in what is generally termed a separation system. The separation system includes a downstream catalyst process path, which is the path the catalyst is exposed to during separation and/or recovery from the reaction solution.
FIG. 1
is one illustrative example of such a prior art hydroformylation system. In
FIG. 1
the reactor is designated as numeral
10
and the separation system is generally designated as numeral
12
. Generally, the reactor
10
includes a continuous stirred tank reactor (CSTR). Optionally, additional equipment may be employed as part of the reactor
10
to increase the conversion of the olefinic compound to aldehydes. To produce C4 aldehydes, feed propylene (PPY) is conveyed via first inlet means to the reactor
10
. Hydrogen (H
2
) and carbon monoxide (CO), often supplied as a gas mixture, better known as oxo gas or synthesis gas are typically introduced via a second inlet means to the hydroformylation reactor
10
or its associated additional equipment. Generally, the H
2
and CO concentration in the oxo gas is about 1:1 molar ratio. The main controlling limitation for the overall propylene conversion is the purity of the propylene or synthesis gas feed stream. If the feed stream is of low purity, then the overall conversion of propylene to C4 aldehydes becomes lower. In the instance where the low purity propylene or synthesis gas is used with its low conversion, additional equipment suitably adapted to provide further conversion of the propylene or synthesis gas may be employed. Thus, while the reactor
10
is shown simply as a block in
FIG. 1
the reactor may include various unit operations commonly employed in conventional hydroformylation reactor systems.
The aldehyde products are generally separated and recovered from the reaction solution in the separation system
12
. Many types of separation systems
12
are utilized in the prior art hydroformylation systems. For example the aldehyde products may be separated and/or recovered from the hydroformylation reaction solution by composite membrane techniques, or optionally by the more commonly used vaporization separation techniques of distillation, such as single or multiple stage distillation under reduced, normal or high pressures, as applicable in an aldehyde removal unit
14
. Condensation of the volatilized materials and separation and further recovery thereof may be carried out by conventional means, and the remaining reactants and optionally additionally the solvents contained within the reaction solution may be separated in solvent recovery unit
16
and recycled back to the hydroformylation reactor. Such types of continuous hydroformylation systems are well known in the art and thus need not be described in further detail here. Examples of such continuous prior art systems can be found in U.S. Pat. Nos. 5,087,763 and 5,865,957.
These continuous hydroformylation systems suffer from the build-up of detrimental by-products. Specifically, during the hydroformylation process, other reactions occur in addition to the formation of aldehydes. Many higher boiling point components such as dimers, trimers, tetramers of aldehydes and the like are formed as a by product of the reaction. These high boiling point by-product components (hereinafter referred to as “high boilers”) are detrimental to the process and severely reduce the aldehyde yield. Thus, in the prior art systems it is necessary to remove them from the hydroformylation reactor effluent stream. The high boilers are removed in a variety of conventional techniques, such as by employing one or more a high boiler separation units, such as that described in U.S. Pat. No. 5,648,554, where vaporization or distillation in one or more stages distillation under normal, reduced or elevated pressures is used. Thus, it is highly desirable to provide a method wherein the formation of high boilers are reduced and/or minimized.
An important aspect of the hydroformylation process is the catalyst utilized to assist the hydroformylation reaction. It is common to use a soluble complex of an element selected from Groups VIII to X of the Periodic Table (hereinafter referred to as a “Group VIII metal”) having an organic phosphorus compound as a ligand. In general, the ligand used together with the metal component of the catalyst gives substantial influence to the catalytic reaction. Rhodium (Rh) is commonly used as the metal component of the catalyst. Rh will form a complex molecule with the ligand which activates the hydroformylation reaction. Significant effort has been focused on the development of catalysts as demonstrated by U.S. Pat. Nos. 4,668,651, 5,113,022, 5,663,403, 5,728,861, among others. Unfortunately, however, this complex molecule decomposes during the reaction at a significantly high rate such that the spent or deactivated catalyst must be removed from the reactor and replaced with new, activated catalyst. In prior art systems the catalyst may be removed by conveying the catalyst via a downstream catalyst process path into the separation system
12
, such as by employing a split stream from the bottom of the high boilers separation unit
18
and conveyed to suitably configured catalyst removal unit
20
. For example, U.S. Pat. Nos. 4,668,651 and 5,113,022 describe a process where the liquid reaction solution is passed to a vaporizer/separator where the aldehyde product is removed via distillation in one or more states under normal, reduced or elevated pressure, and it is preferred to separation the desired aldehyde produce from the rhodium catalyst solution under reduced pressure at temperatures below 150° C. and preferably below 130° C. While the aldehyde product is separated in such process, the inventors have found that much of the catalyst degrades at these relatively high temperatures. Since significant effort and expense is taken to recover the catalyst and particularly the ligand compound,

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